1. Field of the Invention
The present invention relates to an elevator door control apparatus which is capable of quickly reversing the direction (opening/closing) in which elevator doors are moving when door-open buttons or door safety devices, such as safety switches, are operated, thereby increasing passenger safety.
2. Description of the Related Art
FIG. 4 is a block diagram illustrating a conventional elevator door control apparatus disclosed in, for example, Japanese Patent Laid-Open No. 2-123088. In FIG. 4, a microcomputer 2 (hereinafter referred to as a main computer) for controlling an elevator, disposed within a control panel 1, is connected to a door control circuit 4 through a control cable 3. The door control circuit 4 includes a microcomputer 5 (hereinafter referred to as a door computer) for controlling doors, a motor control circuit 6 and a motor drive circuit 7. A door motor 8 for opening/closing a pair of doors 14, a pulley 9 for a speed reducer, a rotor 10 and a belt 11 are disposed in the upper section of an elevator car 17. The pair of doors 14 are connected to the belt 11 via connection sections 12 and 13, respectively. A SHOE switch 15 and a door-open button 16 inside the car 17 are electrically connected to the main computer 2 and the door computer 5 through the control cable 3. The car 17 is moved upward and downward by a traction machine 19 through a rope 18 while being balanced by a counterweight 20.
Referring now to the timing chart of FIG. 5, the operation of the above-described apparatus of the prior art will be explained. The cycle of the timing at which signals are received by the main computer 2 is set at 40 ms, and the cycle of the timing at which signals are received by the door computer 5 is set at 10 ms.
It will now be assumed that the door motor 8 is being driven by the door computer 5 to close the doors 14 because the door computer 5 has received a command for closing the doors 14 from the main computer 2. Under this condition, if a signal for discontinuing the door-close operation is generated from the SHOE switch 15 or the door-open button 16 during the period of 10 ms from time T2 to T4, the door computer 5 can receive this signal at timing T3. In contrast, the main computer 2 cannot receive this signal because signal input timings T1 and T5 do not exist between times T2 and T4, during which period the stop signal is generated. Therefore, the state in which the door-close command signal is output to the doors by the main computer 2 does not change.
However, since, as described above, the door computer 5 can receive a signal for discontinuing the operation of closing the doors 14, the door computer 5, in response to this signal, immediately issues a command for stopping the operation of closing the doors 14 to the motor control circuit 6, causing the door motor 8 to be stopped by means of the motor drive circuit 7. As a result, the speed of the operation of closing the doors 14 is reduced during the period from time T3 to T4 and the doors 14 stop. The door computer 5 receives a command from the main computer 2 at timing T6 after the doors 14 are placed in a stopped condition for a predetermined time, and controls the opening/closing of the doors 14 in accordance with this command.
On the other hand, since the main computer 2 cannot receive signals from the door-open button 16 or the SHOE switch 15, and the state of the main computer 2 in which the door-close command is output is unchanged, the door computer 5 receives this command at timing T6 and immediately issues a command for closing the doors 14 to the motor control circuit 6 in order to control the driving of the door motor 8. As a result, the doors 14 are accelerated in a direction in which the doors 14 are closed from timing T6, and are thus closed.
If input timing of the main computer 2 exists in the period during which a signal for discontinuing the operation of closing the door 14 is generated, the doors 14 are discontinued by the same sequence as described above and then reversed to the direction which the doors 14 are opened.
In the conventional elevator door control apparatus described above, operation signals of a SHOE switch (a door safety device) or the like are received by both the main computer 2 and the door computer 5, the door computer 5 stops the operation of the doors 14 by itself while the computation by the main computer 2 is delayed. That is, the doors 14 are temporarily operated irrespective of the command of the main computer 2. For this reason, there is a problem described below.
For example, if, after the operation of a door fully-close switch for detecting the fully-closed condition of a door is confirmed, a brake of an elevator is released and the elevator is activated, the activation of the elevator is delayed by the operation time of the brake. For this reason, an elevator is provided which has a position switch for detecting that a door is positioned near a fully-closed position, the brake beginning to be released in accordance with the operation of the position switch, and the elevator being activated by the operation of the door fully-close switch. In this case, if a safety device, such as a SHOE switch, is operated or erroneously operated when the door which is being closed is positioned between the position switch and the door fully-close switch, and the door is stopped by the door computer 5, the door fully-close switch is not operated. Therefore, an extremely dangerous condition arises in which the brake is released by the operation of the position switch in spite of the fact that the elevator cannot be activated. Thus, there is a problem as regards safety.
In addition, there is another problem in that the number of control cables 3 corresponding to the number of safety devices is required to input operation signals of the safety device to both the main computer 2 and the door computer 5, thus increasing the cost of the apparatus.